Radio noise

[M Towsley]

Re: Radio noise

Darryl,

After doing the cans and the shielded wires and lower shielded plugs the popping could be squelched out. I recently redid my instrument panel and interior and once I got a good look at the old P-Leads I knew I needed to make new ones. Using new shielded wire, (the white shielded aircraft wire), and grounding them at the mag only I no longer have any popping. I even lowered the squelch and still nothing. There is some debate regarding grounding at the mag only or mag and magneto switch, but after doing some research I decided to ground the shielding at the mag only. The other thing I did was to use a magneto 'can' at the magneto switch, which also is grounded. I had a picture of it, I will try and find it and post it. The can was purchased off of Ebay. One shows up now and then.

[M Towsley]

Re: Radio noise

This is a link to Barnstormers showing an A7 switch with the shielding can.

http://www.barnstormers.com/classified_651787_AAF+TYPE+A7+Magneto+Switch.html

[Hank Jarrett]

Re: Radio noise

Marty,
Interesting about shielding one end of the P leads. Did you ever try connecting a short between the Mag can and the P lead to see if anything changed?
Hank

[M Towsley]

Re: Radio noise

Hank,

I did a lot of research on this. The general consensus was that both ends of the P leads shield did not need to be grounded. When I made the new wires I did not make a shield ground lead off of the magneto switch end of the P leads. The switch 'can' is grounded to the magneto switch ground and, of course, the magneto switch ground is then grounded to the aircraft. At the mag side the P leads are mounted to the bolt and the shield part of the P leads is grounded to the ground screw located on the magneto. After yesterdays test I found good results.

It would not be difficult to go ahead and make ground leads for the shield and then attach them to ground at the switch when originally making the leads.

Here is a link to a website that shows you how to make P leads and how to ground the shielding. I chose to not make the P lead portion un-shielded as long as is shown on the attached link as I wanted to keep the shield around the wire as much as possible. http://www.verticalpower.com/forums/...ing-to-magneto

[flyguy]

Re: Radio noise

My lower ignition system is quiet, my upper one is very noisy.

The only thing different about my upper ignition system and my lower one is cans vs resistive, shielded plugs. Therefore the problem is: the cans (with C26 non-resistive plugs) do nothing to kill the high frequency part of the spark.

If you kill the high frequency part of the spark at the source (the plug gap) then you don't have to be concerned with where it will be conducted or radiated--it isn't there to start with. That is what the resistor part of the shielded plug does.

Eliminate the high frequency part of the spark at the source and you don't have to worry about isolating leads, shorting things to ground, locating your antenna more remotely, or using a radio with a (suppression feature?).

To back up my statements I give, as a simple example, the automotive ignition systems that do not use shielded plugs or wires. They just get rid of the problem with resistance only, and are very quiet.

Like most problems the best resolution comes by reducing to basics and clobbering the basic part.

My problem is that I just hate cutting holes in my top cowling to install resistive plugs, but that is still the best-don't fiddle with it, just fix it- solution.

DC

[woodmw]

Re: Radio noise

Marty,

When do we get to see pictures of and particulars about the new interior/panel?

Darryl,

After doing the cans and the shielded wires and lower shielded plugs the popping could be squelched out. I recently redid my instrument panel and interior and once I got a good look at the old P-Leads I knew I needed to make new ones. Using new shielded wire, (the white shielded aircraft wire), and grounding them at the mag only I no longer have any popping. I even lowered the squelch and still nothing. There is some debate regarding grounding at the mag only or mag and magneto switch, but after doing some research I decided to ground the shielding at the mag only. The other thing I did was to use a magneto 'can' at the magneto switch, which also is grounded. I had a picture of it, I will try and find it and post it. The can was purchased off of Ebay. One shows up now and then.

[M Towsley]

Re: Radio noise

Just took some today. I really need to get the plane in natural light rather than using the flash. If tomorrow is good the wife and I will take a little trip and hopefully I can get some shots outside.